patch applied (ghc): Fix Trac #2494: tcSimplifyRuleLhs
Simon Peyton Jones
simonpj at microsoft.com
Mon Aug 11 06:53:47 EDT 2008
Mon Aug 11 03:44:38 PDT 2008 simonpj at microsoft.com
* Fix Trac #2494: tcSimplifyRuleLhs
tcSimplifyRuleLhs is a cut-down constraint simplifier, intended for
use in RULE left-hand-sides. But it was written before implication
constraints, and the exmaple of this bug report shows that when higher
rank types are involved we need to be a bit cleverer.
The whole business of simplifying constraints on rule LHSs is a bit
of a hack; but for a good reason. See the comments with tcSimplifyRuleLhs.
This patch at least cures the crash.
M ./compiler/typecheck/TcSimplify.lhs -10 +37
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